(i) Technical Field
This invention relates to an image formation apparatus of a printer, a copier, a facsimile, or the like.
(ii) Related Art
In this kind of image formation apparatus, a charging device for applying a bias voltage with an AC voltage superposed on a DC voltage for uniformly charging a photoconductor is widely used. It is known that if the AC voltage in the bias voltage is lowered to a value at which the photoconductor surface potential becomes a saturation point or less, an image defect (image chip, color change, etc.,) caused by uneven charging of the photoconductor occurs and the quality of an output image is degraded.
On the other hand, an art of using a high-hardness material for the surface layer of a photoconductor to suppress abrasion of the surface of the photoconductor for prolonging the life of the photoconductor is also known. However, if abrasion of the photoconductor surface is suppressed, a corona product is deposited on the photoconductor surface and causes an image defect (image chip, color change, etc.,) to occur. To suppress occurrence of the corona product, the AC voltage applied to the photoconductor needs to be lowered; however, if the AC voltage is lowered to the value of the saturation point of the photoconductor surface potential or less, an image defect caused by uneven charging occurs as described above. In all the related arts described above, it is difficult to suppress both of uneven charging and occurrence of a corona product.